The whole of Siam lies between the Tropic of Cancer and the Equator and is subject to the typical monsoonal climate of southeastern Asia, by which the prevailing winds, from the latter part of April to the middle of October, consistently blow from the southwest and from mid-October to April, from the northeast. In Northern, Central, and Eastern Thailand there are three distinct seasons—the hot weather, the rains, and the cold weather, the first extending from February or March to May, the second from June to October, and the third covering the remaining months of the year. When the northeast winds blow strongly, the cold weather is very marked, but at such times as the seasonal winds fail, the cold weather is scarcely distinguishable from the hot. In Northern Siam, which lies at greatest distance from the sea and possesses greater radiation, the days may be hot even during the cold weather when the night temperatures afford a strong contrast by dropping to as low as 50° F. and on the mountains even lower, although never reaching freezing temperatures. The basin of Eastern Siam, with its thin vegetation and cut off from cooling breezes by its surrounding rim, is subject to terrific heats during the day and, during the winter, very low temperatures at night. The central plain, outside of Bangkok, is pleasantly cooled during the hottest season by the continuous sea winds, night and day; in Bangkok, however, perhaps owing to houses of masonry in place of thatch and the drainage of surrounding marshes, the climate is not only appallingly hot but actually becoming perceptibly more so year by year. Peninsular Siam has the mildest and most equable climate, the greatest annual rainfall, and only two noticeable seasons—the hot weather from February to August and the rains from September to January, with the peak of the wet season coming in December.
Owing to the fact that the political frontiers have little relationship to biogeographical boundaries, the Kingdom possesses a fauna and flora richer than those of most areas of comparable size. The primeval jungles of the western and northern mountains show untrammeled Nature at her tropical best. The slopes are enlaced with countless streams and waterfalls, from roaring torrents to rills which flow only during and after the rains. In the forests of these hills and valleys, huge epiphyte-laden trees, bound together by vines, shelter such animals as the elephant, the tiger, and the gaur, but so dense is the cover that the presence of large game is more often made known by signs than by actual sight, and only the hunter who is willing to work hard and long is likely to shoot a worth-while trophy. More than 1,000 different birds are recorded from the country, while fishes of almost endless variety abound everywhere, from the Gulf to the smallest roadside ditches. The natural vegetation ranges from the most typically tropical plants, such as the mangosteen, to forms of the Temperate Zone, such as pines and violets, on the northwestern mountains. The central plain, where not devoted to rice cultivation, shows the characteristic flora and fauna of a marsh and the eastern plateau has an impoverished biota, characterized by a certain number of endemic forms; the Peninsula, however, like the west and north, bears great forests rich in species of animals and plants.
PEOPLES
Archeology can still tell us little of the first human occupants of Siam. The earliest evidence of man's existence here is furnished by celts, uncovered in the Peninsula and on the eastern plateau, which are supposed to date from the later Neolithic period; geology, however, gives us no reason to conclude that the makers of these implements were not preceded by other races.
[Illustration: 1. The rivers fall from the northern plateaus to the central plain through narrow defiles.]
[Illustration: 2. Ancient wall at Chiengmai. The city walls are preserved as picturesque ruins.]
[Illustration: 1. An international incident was caused by the European alpinist who first scaled the monolith to plant his nation's flag upon it.]
[Illustration: 2. Boats must be pulled upstream through the rapids by ropes.]
[Illustration: 1. The valuable gum resin, Bengal kino, is yielded by the "mai kwao" (Butea frondosa).]
[Illustration: 2. Young rice plants are transplanted from a seedbed to the flooded fields.]